The present invention relates generally to front end rate shaping during fuel injection events, and more particularly to a valve concept for producing boot shaped injection rate trace profiles.
Over the years, engineers have come to recognize that undesirable emissions can be lowered at different operating conditions by producing particular injection rate trace profiles. Among the various rate shape profiles are so called ramps, boots, squares and splits, etc. There are numerous references describing various fuel injection systems and the means by which they can produce one or more of the above identified rate shaping traces. For instance, commonly owned U.S. Pat. No. 5,462,030 to Shinogle shows a spring loaded device that can be employed in a fuel injection system in order to produce a front end rate shape that is somewhere between a boot and split injection rate trace. During an injection event, as fuel pressure is building after the nozzle outlet has opened, the Shinogle device includes a small spring loaded accumulater volume that opens at some pre-determined pressure. As fuel flows into the accumulater volume, the pressure, and hence the flow rate, at the nozzle outlet briefly drops. After the accumulator volume is full, the pressure and flow rate out of the nozzle outlet rise in a somewhat conventional manner. The end result is a particular front end rate shaping that is a function of several factors including the accumulator volume, its opening pressure, etc. The Shinogle device also appears to include some adjustment means for adjusting the rate shape produced by the device. While the Shinogle device appears to have a promise, there remains room for improvement.
The present invention is directed to these and other problems associated with producing front end rate shaping in fuel injection systems.
In one aspect, a fuel injector includes an injector body that defines a nozzle supply passage and a nozzle outlet. A needle valve member is positioned in the injector body and is moveable between an open position in which the nozzle supply passage is open to the nozzle outlet, and a closed position in which the nozzle supply passage is closed to the nozzle outlet. A nozzle supply valve member is positioned in the injector body and includes an opening hydraulic surface exposed to fluid pressure in an upstream portion of the nozzle supply passage. The nozzle supply valve member is moveable between a first position in which the nozzle supply passage is relatively restricted, and a second position in which the nozzle supply passage is relatively unrestricted.
In another aspect, a fuel injection system includes a nozzle supply valve moveable between a first position in which a nozzle supply passage is relatively restricted, and a second position in which the nozzle supply passage is relatively unrestricted. The nozzle supply valve is biased by a first biaser toward its first position when fluid pressure in the nozzle supply passage upstream from the nozzle supply valve is below a first predetermined pressure. A nozzle outlet valve is moveable between an open position in which the nozzle supply passage is open to a nozzle outlet, and a closed position in which the nozzle supply passage is closed to the nozzle outlet. The nozzle outlet valve is biased by a second biaser toward its closed position when fluid pressure in the nozzle supply passage between the nozzle supply valve and the nozzle outlet valve is below a second predetermined pressure. The second predetermined pressure is lower than the first predetermined pressure.
In still another aspect, a method of injecting fuel includes a step of opening a nozzle outlet at least in part by raising fuel pressure in a nozzle supply passage above a first predetermined pressure, and moving a needle valve member from a closed position toward an open position. Fuel flow in the nozzle supply passage is restricted. The flow restriction in the nozzle supply passage is then removed at least in part by increasing fuel pressure in the nozzle supply passage above a second predetermined pressure, which is greater than the first predetermined pressure, and by moving a nozzle supply valve member from a first position toward a second position.